Television method and arrangement for carrying out the same



May 22, 194:'. HANNs-HEINZ WOLFF Y2,376,645

TELEVISION METHOD AND ARRANGEMENT FOR CARRYING OUT THE SAME Filed Aug. 5j 1938 3 Sheets-Sheet 1 May 22, 1945"R HANNs-HEINZ woLl-F 2,376,645

'IE.EV|SIONY METHOD AND RRANGEMENT FOR CARRYING OUT THE SAME Filed Aug. 5, 1938 3 Sheets-Sheet 2 May 22, 1945 HANNs-HEINZ woLFF 2,376,645

TLEIISION'A METHOD AND ARRNGEMENTI` FOR CARRYING OUT THE SAME 'Filed Aug. 5, 195s 3 Sheets-Sheet 5 fatentecl May 22, 1945 TELEVISION METHOD AND ARRANGEMENT FORCARRYING OUT THE SAME Hanns-Heinz Wolff, Berlin, Germany; vested in the Alien Property Custodian Application August 5, 1938, Serial No. 223,270 In Germany August 12, 1937 8 Claims. (Cl. P18-6.8)

This invention relates to improvements in television systems.

It has already been proposed to make use of the storage principle, the application of which more particularly to the transmission end has recentlybecome widely known (compare, for example, the ikonoscope), also 'at the receiving end, i. e., to produce received television images in such fashion that a plurality of image points, for example an entire line, or preferably even the entire image, are visible simultaneously.

The proposals made in this connection had the object of increasing the light intensity of the received television'image.

The present invention more particularly relates to a television system of this nature making use of storing devices at the receiving end, and is based on the new recognition that by storage of the light impressions at the receiving end the tendency of the image to ilicker is reduced. In this connection it isto be observed that in television receiving apparatus of this nature a darkening of the entire field image at times is wholly eliminated, so that television receiving means of this character, from the point of view of elimination of the flickering, possess even more favourable characteristics than a normal film. It is .known that the darkening action, which is necessary in cinematograph films after al; sec. for the advance of the film, would lead to a flickering `effect if a remedy had not been obtained by the fact that between each two unavoidable darkening actions of this kind there is included an additional darkening action, so that there are 48 darkening actions per second. It has been usual heretofore to assume that requirements of this nature require to be applied automatically to television receivers, since the characteristic properties of television receiver, from the point of view of eliminating the iiickering effect, have been considered as essentially more unfavourable than those of a cinematograph film, in which at least each single picture is projected on principle in its entirety. 'I'he situation is different, however, in the case of television receivers operating with storage of the light impression, particularly if the storage takes place over an entire image period. In receivers of this kind the image excitation of each single element of the picture endures for such time until it has been replaced by a different image excitation. Fundamentally, a complete darkening of the image field1 such as is unavoidable in a cinematograph nlm, does not occur in i television receivers of this nature.

It has also been assumed that 24 image changes per second are necessary so that movements will not be blurred upon the reproduction. It has been found, however, that this is not the case.

`It is well known that in the case of an insuflicient number of image changes there is created the impression of a staccato movement. It hasbeen found that the impression of movement aC- quires fluency with a number of image changes amounting to approximately 10 per second, and lms with 12 image changes per second are in this respect quite faultless (the fact that they are not free from flickering has nothing to do with this). If now 12 single pictures per second are replaced by 24 pictures per second, it is true that sharper single pictures are obtained, but this greater sharpness of the single picture has subjectlvely no eect, as two successive pictures already appear to flow one into the other in the case of 12 single pictures per second.

Whereas, therefore, for television purposes, image changes amounting to approximately 32 per second have been considered absolutely essential heretoiore, and even with image changesin this number a satisfactoryv elimination of the flickering effect was not to be established, so that generally speaking there has been adopted the method of scanning in interlaced groups of lines with 48 lto 50 half-scannings, it is possible in accordance with the invention when employing a storage system at the receiving end to obtain satisfactory pictures even with approximately 12 scannings of a simple kind.

'The recognitions described in the above technically utilized by the present invention.

Accordingly, it is an object of the present in.- vention to provide in a television system a transare mitting apparatus comprising means for transmitting image signals with an image ciwge frequency not exceeding approximately 12 per second, and preferably not less than 10 per second, in combination with a receiving apparatus comprising means for simultaneously producing a plurality of pictures of image elements.

It is a further object of the presenty invention to provide improved television transmitting apparatus ofthe just mentioned type in -the television system referred to.

It is a still further object of the present invention to provide improved television receiving apparatus of the just mentioned type in the vision system referred to.

Other objects of the invention will become apparent from the following detailed description and from the appended claims in connection with telethe accompanying drawings, in which, in a purely y transmitted to the receiver.

elements of a scanning device comprising two rotatable apertured discs for realizing the invention in television transmitters for transmitting cinematograph films,

Figs. 4a-4e show the same elements as Fig. 3 at diiferent moments to illustrate their manner of operation, w

Fig-5 represents another arrangement of the discs shown in Figs. 3 and llaf-4e,

Fig. 6 shows a view similar to that of Fig. 2 of another scanning disc, and

Fig. 'I illustrates the paths of the scanning light spot over two successive film pictures caused by an arrangement according to Fig. 6.

Referring now to the drawings, the invention will be rst described in conjunction with the diagram given in Figs. 1a and 1b. In Fig. 1a Rs is a device for deriving television signals from the optical image of a visual object at the transmission end, which is shown as electron camera according to the storage principle with cathode ray scanning, comprising the cathode Ks, the anode A5, the deiiecting plates Ps and the picture screen S5. In Fig. 1b, Re is a receiving tube producing a persistent image, such as the applicant has already described in a number of earlier applications, and which possesses a cathode Kg, an anode Ae, deflecting elements Pe. a grid G consisting of metallic elements insulated one against the other and acting as a control electrode for a large surface cathode BK, an electron-optical system O for large-surface reproduction, and a luminescent screen Se. At the transmission end there is a device for producing the scanning frequencies, which according to the invention are equal to approximately 12 per second, or 12u per second (n being the number of lines per image), and are impressed on the synchronisation impulse generator. duced serve, on the one hand, to synchronise the deiiecting potentials produced in the scanning potential generators, and on the other hand they are conducted to the amplifying and modulating system to be impressed on the carrier wave and The scanning potentials are impressed on the scanning system Ps. The signal plate of the mosaic screen Ss is coupled to the amplifying and modulating system, in such a manner that the signals representing the contents of the image are also impressed on the carrier wave. At the receiving end the received signals are ampliiied and rectified, the signals representing the contents of the image are separated from the synchronisation signals and ampliiied and modulate at the anode Ae the speed of the cathode ray, so that by way of secondary emission charges dependent on the image modulation are imparted to the single elements of the grid G. The synchronisation signals are amplined and synchronise the scanning potential generator, which supplies deflecting potentials for the system Pc. The modulated cathode ray accordingly passes over the grid G synchronously with the scanning ray in the transmission tube Rs, so that the charges of the grid G correspond in their geometric distribution to the distribution of light of the transmitted image. The emission of the image cathode BK is controlled according to the charge distribution at the grid G, and the electron-optical reproduction of the cathode BK on the luminous screen Se accordingly produces an image corresponding to the image transmitted. The receiving tube described is designed in accordance with proposals of the applicant.

The synchronisation impluses pro-- It is assumed that the arrangement operates withv continuous advance of the lm. In this embodiment of the invention the direction ofmovement of the lm is selected to be from the bottom towards the top, as indicated by the arrow. The spiral-aperture disc rotates in such fashion that apertures pass successively over the film which are positioned higher and higher. The rate of movement of the nlm, however, is selected to beA so high that nevertheless a scanning takes place from the top to the bottom of the picture, i. e., the iilm is moved twice as quickly in the upwards direction as the strip drawn by the scanning apertures is shifted upwards during the rotation of the disc. In the drawings there are shownthc positions of a particular lm picture at a time which is considered equal to "0 and one-twelfth of a second later. At the time t=0 the inner end point of the spiral just commences to scan the upper edge of the picture in question. At the time t=11 sec. the outer end point of the spiral just completes the scanning of the bottom line of the same picture. At this moment the inner end point of the spiral commences the scanning of the next picture but one. The picture situated between the two is not scanned at all, as was the intention. 1

According to a' further feature of the invention, an interlaced line scanning of films can be so carried out that of each two successive pictures the one is scanned in one group of lines and the picture.

other in a group of lines staggered in relation to the rst group, the first picture, for example, along the lines 1, 3, 5 the second picture along the lines 2, 4, 6 the third picture again along the odd lines, and the fourth picture along the lines of even number, and so forth.V

An example ofv an arrangement for carrying out this idea is illustrated diagrammatically in Figs. 3 and ia-4e, whilst Fig. 5 shows in relation to Fig. 3 a somewhat modified arrangement.

In the embodiment of the invention illustrated in Figs. 3 and 5 there is employed a scanning disc Si having a circle of 2n apertures, assuming n to -be the number of apertures for a group of lines. The distance between two adjacent apertures amounts to b/2, if b is the Width of the It is assumed that the lm is moved past the disc in such fashion that two apertures, which are spaced apart to an extent equal to the entire width b of a picture scan two lines which are separated from each other by the width of a line. By means of a special shutter arrangement care is taken that during the scanning actions the last two apertures referred to the aperture between the same is unable to perform scanning. For this purpose there is provided a further rotary disc S2 having a rim of n apertures. The width of each aperture of the disc Sz-is equal to one-half of the width of the picture, i. e., is equal to b/2. The distance between each two adjacent ones of said apertures is also equal to b/2. Their height is made approximately equal to but preferably greater than the height of a scanning aperture in the disc S1.

The operation of the diaphragm S2 will be described in conjunction with Figs. raf-4e. As starting point there is taken the time 15:0, when the aperture I of S1 commences to scan the surface of the picture. It is assumed that at this moment the disc S2 is in such a position that the aperture I is just situated atthe left hand edge of a shutter aperture of Sz. Each of the remaining scanning apertures of S1 of odd number is also situated at the left hand edge of the appertaining apertures of S2. yThe scanning apertures of even number are covered at this time. N represents the number of revolutions of the disc S1 per second. According to the invention N is selected to be approximately equal to 24, from which there then result approximately 12 complete scanning actions per second. At the phase l #tra aperture 3 commences to scan the image area,

and owing to the variation in the meantime of the position of the film, along the third line. In the meantime the disc S2 has also continued to rotate, in the same direction as the disc S1 and almost at the same speed, although somewhat more slowly, so vthat the left hand edges of its apertures now lag to a slight extent behindv the scanning apertures.

At the phase 1 #hat Athe aperture bearing the number Zk-I-l' comthe aperture I would again just commence its scanning action., At this moment, however, it is darkened, and cannot perform scanning. Following a further half line period, however, the aperture 2 commences to move over the surface of the picture. In the meantime the film has been advanced by the width of a line in the upward direction, and the aperture 2 accordingly scans the second line of the picture, which upon the scanning by the apertures of odd number remained unscanned. This scanning by means of the apertures of even number, however, relates to a different picture to that in the scanning by the apertures of odd number because vin the meantime the lm has been advanced exactly to the extent of one frame.

In viewing Figs. 4a-4e it will be seen that during a revolution of the scanning aperture disc S1 the diaphragm Sz must have lagged behind by the amount b/2 along the perpihery in question. This portion is equal to the 211th part of the complete periphery concerned; If f1 is the rotation frequency of thedisc S1 and fz the rotation frequency of the disc Sz, there `results If, for example, there is assumed a scanning operation in two groups of lines each comprising 200 lines, it is shown that the frequencies of the two discs require to differ by .25%. In the case of 11:24, the example selected above, the difference in frequency accordingly .amounts to curacy by stroboscopic methods.

It is not necessary to arrange the two discs S1 and S2 coaxially, as-shown in Fig. 3. The arrangement can also Abe as indicated in Fig. 5.

When using the arrangement described in the above a certain difficulty arises insofar as the scanning of the second group commences, not one line period but one and a half line periods after completion of the scanning of the first group (compare Figs. id-4e; scanning is not commenced at the time characterised by lc=n, but at the time characterised by k=n+ 1/2). In the same manner scanning of the third group is delayed in relation to the second group. In a change over between two groups of lines there is always a delay of one-half of a line period, and since the movement of the lm is not affected by this delay and the film pictures accordingly move past the scanning line at a rate equal to N pictures per second, the point of location of the gap between two scanned groups is gradually shifted over the surface of the picture.

This lack of synchronism can be eliminated according to an additional feature of the invention by the use of the arrangement described in the following in conjunction with Figs. 6 and 7, which arrangement also has the advantage of greater simplicity, as in the same a special diaphragm is not required. The scanning apertures in the scanning disc are selected to be odd in number, equal to 2n+l. If the film has been taken with 24 pictures per second, the disc rotates with a velocity of rotations of 12 per second, whilst the film is moved at such a speed that 24 pictures per second are conducted past the scanning line. In the period of time, therefore, in which al1 21H-1 apertures have been moved once past the film area two nlm pictures have passed over the scanning line. As shown in Fig. '7, this results in the fact that if the rst aperture commences to scan exactly in the upper corner of a picture, the n-I-lst aperture cuts the lower edge of the picture at the centre and it covers the second half of its scanning path in the next picture. The 1L+2nd aperture does then not scan the rst line of the picture in question, `as does the first aperture, but the second line. The groups of lines in which two consecutive pictures are scanned are interlaced, which means that the lines of the one group in relation to the appertaining picture are disposed between the lines of the other group in relation to the picture appertaining to this group. It is to be observed that for carrying out the fundamental idea of transmitting upon the scanning of lms only every second lm picture, `and also in carrying out the idea, upon the scanning of interlaced groups of lines, of assigning each lgroup of lines to another picture, other arrange-v ments would also be possible to those discussed in the above. The fundamental ideas of the present invention arenot limited to the described embodiments. l

The great significance of the present invention resides above all in the fact that it greatly cuts down the width of the frequency band in the transmission. From this there result inter alia the following technical advantages:

1) Considerable simplification and cheapening of the receiver connection system (smaller demands on the band illters, etc.),

(2) Simplification of the side band problem.

(3) Possibility of a longer carrier wave, and in consequence (a) Relaxation of the demands on connection, aerial design, etc., at the transmission and receiving ends imposed by the shortness of the carrier wave,

(b) Greater range of the television transmitter and less effect on the 'rectption by elevations of the ground or the like between the transmitter and the receiver.

I claim:

1. In a television transmitting apparatus for `transmitting a cinematograph film, a scanning device for performing an interlaced scanning with at least two groups of lines, said scanning device comprising a rotatable disc having a Acircle of scanning apertures, the number of scanning apertures of ,said disc being equal to the number of lines of a total scanning in interlaced groups, a movable shuttering device adapted to obturate at each moment those scanning apertures of said disc which do not belong to the group of lines just being scanned and to let unobturated the other apertures of said disc, and means for continuously moving said nlm at such a rate that the spacing measured in widths of a line of two strips drawn by two consecutive scanning apertures of said disc which belong to the same group of lines is equal to the number of groups less one.

2. In a television transmitting apparatus for transmitting a, cinematograph film, a scanning device for performing an interlaced scanning with at least two groups of lines, said scanning device comprising a rotatable disc having a circle of apertures, the number of apertures of said disc being equal to the number of lines of a total scanning in interlaced groups, a second rotatable disc for partly obturating the apertures of said rst disc, said second disc having a rim of apertures, the number of apertures of said second disc being equal to the number of lines per group, said iirst and said second disc being so arranged with respect to one another that upon the revolution .of said second disc its apertures move along' substantially the same path as the apertures of said first disc, and thatat each moment only one group of apertures of said flrst disc corresponding to one group of lines is unobturated,

means for rotating said first and said second disc at such a rate that the circumferential velocity of said second disc differs from that of said first disc by such an amount that after one revolution of said rst disc said one group of apertures is obturated and the next one is unobturated, and means for continuously moving said film at such a rate that the spacing measured in widths of a line of two strips drawn by two consecutive apertures of said rst disc which belong to the same group of lines is equal to the number of groups less one.

3. In a television transmitting apparatus for transmitting a cinematograph film, a scanning device for performing a two-intercalation scan with two groups of lines, each of said groups comprising n lines, said scanning device comprising a rotatable disc having a circle of 2n apertures,

a second rotatable disc for partly obturating the apertures of said ilrst disc, said second disc having a rim of n apertures, each of which has a width equal to one half of the width of a film picture and is spacially disposed from the adjacent aperture by one half of the width of a film picture, the height of each aperture of said second diaphragm being at least equal to the height of the aperture of said first diaphragm, said first and said second disc being so arranged with respect to one another that upon the revolution of said second disc its aperture moves along substantially the same path as the apertures of said rst disc, and that at each moment only one group of apertures of said rst disc corresponding to one group of lines is unobturated, means for rotating said rst and said second disc at such a rate that the circumferential velocity of said second disc diiers from that of said iirst disc by such an amount, that after one revolution of said first disc said one group of apertures is obturated, and the next one is unobturated, and means for continuously moving said lm at such a rate that the spacing of two strips drawn by two consecutive apertures of said first disc which belong to the same group of lines is equal to the width of one line.

4. The invention set forth in claim 3, wherein the velocity of rotation of said second disc is in a ratio of 2n-1z2n to that of said iirst disc.

5. The invention set forth in claim 2, wherein said second disc is arranged co-axially with said first disc.

6. In the television art in combination a transmitting apparatus comprising means for transmitting image signals with an image change irequency not exceeding approximately 12 per sec., and a receiving apparatus comprising a cathode ray tube provided with a luminescent screen, with means for producing a radiation for exciting said screen, and with a control electrode adapted to store electric charges corresponding to said image signals substantially during one complete image change period, for controlling said radiation.

'7. In a television receiving apptratus comprising a cathode ray tube in combination a luminescent screen, a large surface cathode adapted to emit an electron stream, means for directing said electron stream towards said screen, a control electrode of mosaic structure for controlling the intensity of said electron stream, said control electrode being adapted to store electric charges substantially during one complete image change period, means for producing a primary cathode ray, means for focusing said primary cathode ray on said control electrode, means for causing said cathode ray to impress charges corresponding in their amount to the intensity of the received image signals on'said control electrode, and means for deflecting said cathode ray to scan said control electrode with an image frequency not exceeding approximately 12 per sec.

8. In a television transmitting apparatus for transmitting a cinematograph nlm, a scanning device comprising a rotatable disc having a spiral of apertures, the rst and the last aperture of said spiral having a radial distance from one another which is exactly equal to the height of a iilm picture, and means for continuously moving said film in the direction in which the strips drawn by the scanning apertures of said disc are shifted upon the rotation of said disc and at twice the speed at which said strips are shifted.

HANNS-HEINZ WOLFF. 

